U.S. Sen. John McCain speaks during an interview with Eyewitness News on Jan. 21, 2016.

WASHINGTON (WPRI) – Former Republican presidential nominee John McCain won’t be taking sides in this year’s hard-fought Republican presidential primary, dashing the hopes of some candidates who were eager to win his support.

During an exclusive interview Thursday with WPRI.com, McCain said he has enough to worry about as he works to fend off a conservative primary challenger in his home state of Arizona. McCain is up for re-election in November.

“I’m not going to endorse anyone,” McCain said. “I’ve got my own race to run, which I view as being a very, very tough race and a great challenge, and I’ve got to spend my time and effort in what’s going to be a very tough political campaign.”

Pressed on whether he might change his mind, McCain said: “I’ve definitely decided that I won’t endorse in this race.”

McCain’s announcement comes days after his 2008 running mate, former Alaska Gov. Sarah Palin, endorsed businessman Donald Trump for the GOP nomination. CNN reported earlier this week that former Florida Gov. Jeb Bush’s campaign has been hoping to win McCain’s endorsement now that his close friend, South Carolina Sen. Lindsey Graham, has dropped out of the race.

McCain emphasized that his decision not to endorse is no sign of disrespect toward Bush or some of the other hopefuls.

“I have great admiration for Jeb Bush,” he said. “I like Chris Christie. John Kasich and I served together in the United States Senate – he’s been a very successful governor. I’m sure there are a couple others there.”

“So I would be happy with any of those individuals that I mentioned, and I’ll support the nominee of the party,” he said.

McCain declined to comment on former GOP nominee Bob Dole’s comments this week that Donald Trump might be a better choice than Texas Sen. Ted Cruz; both have clashed with McCain in the past.

The first votes in the presidential race will be cast Feb. 1 in the Iowa caucuses.